The electrolytic production of e.g. alkali metal hydroxides is today of considerable importance, although a large amount of energy is consumed in the electrolysis process. Many attempts have been made to lower the energy consumption, e.g. by use of a gas diffusion electrode in the electrolytic cell which is believed today to have the highest capability of saving electric energy and lower the production costs.
When the conventional electrolytic reaction (1) using a hydrogen-evolving metal electrode as cathode is replaced by a gas diffusion electrode, reaction (1) is replaced by reaction (2) as follows:2NaCl+2H2O→Cl2+2NaOH+H2, E0=2.21 V  (1)2NaCl+½O2+H2O→Cl2+2NaOH, E0=0.96 V  (2)
By converting a hydrogen-evolving metal electrode to a gas diffusion electrode, the cell voltage is reduced from 2.21 V to 0.96 V, thus an energy saving of about 60% becomes theoretically possible. Accordingly, various investigations have been conducted for performing chloralkali electrolysis using a gas diffusion electrode.
U.S. Pat. No. 5,938,901 discloses an electrolytic cell partitioned by an ion exchange membrane into an anode chamber and a cathode chamber. The electrolytic cell comprises current collectors electrically connected to horizontal electrode members having the shape of belts arranged with a space between the members in the vertical direction, which electrode members are contacted to the membrane.
However, it has been observed that the electrical contact between the belt-shaped electrode members and the current collectors is not satisfactorily homogeneous, which leads to inhomogeneous current distribution and higher cell voltage, as well as a shorter service life of the gas diffusion electrode. These problems arise especially if the horizontal and/or vertical dimensions of the electrode members are too long.
Furthermore, it has been noticed that partial drying, i.e. vacant portions, may occur in the cathode chamber between the membrane and the gas diffusion electrode due to formation of gaps caused by an insufficient amount of electrolyte filling such gaps. As a consequence of these problems, the cell voltage is often unstable and at a higher level, which shortens the life span of the gas diffusion electrode. The present invention intends to solve the problems mentioned above.